1. Field of the Invention
This invention relates to test kits for detecting acidity in oils and particularly relates to field test kits for detecting acidity in refrigeration oils which are contaminated with a leak detecting component.
2. Review of Prior Art
In the refrigeration industry, lubricating oils are tested for acidity as an indication of suitability for continued use and as a means for detecting contamination of the entire refrigeration system. Such tests are set forth in ASTM D664-58 and ASTM D974-64, but the requirements of D664-58 for laboratory equipment makes this procedure unsuitable for field testing, and testing according to D974-64 is not satisfactory with dark colored samples of refrigeration oils because the color changes that are produced by a color indicator such as p-naphtholbenzein solution are obscured by the color of the sample, making it difficult to estimate color changes with sufficient precision.
Acid field test kits for use on refrigeration and airconditioning systems have been developed to meet this need and are currently designed to show whether or not the acidity of the refrigeration oil is above an acid number of 0.045 to 0.05, as determined by the color produced by an acid/base indicator in the test kit. New refrigeration oils intended for use in refrigeration systems generally have an acid number of from 0.01 to 0.02 when tested according to conventional ASTM test methods. Such an acid number represents the quantity of base, expressed in milligrams of potassium hydroxide, that is required to titrate all acidic materials in a 1 -gram sample of the oil that are dissociated sufficiently to react to the KOH. According to experience, when a refrigeration oil develops an acid content which corresponds to an acid number of from 0.05 to 0.07, it should be replaced with new oil.
There are four acid field test kits which are now in popular use for testing refrigeration and air-conditioning systems. Two of these four field test kits produce a homogeneous mixture after shaking, and two produce a mixture that separates into two phases, the aqueous bottom phase containing the telltale color. The two-phase kits are based upon the method disclosed in U.S. Pat. No. 3,510,260 for forming an aqueous acid solution as an immiscible bottom phase, in which the acidic components are dissolved, with the oil as the top phase. When testing dark oils with a homogeneous-type kit, the color change is obviously likely to be masked. When using the two-phase method, the color change of an indicator solution, such as a one percent solution of phenolphthalein in ethanol, can become easily observable even with a dark oil when the aqueous phase turns from colorless to pink or red. However, if a red-colored leak detector is present as a component of the oil, the color change can be entirely obscured.
For example, when the refrigeration oil is contaminated with a leak detector such as the highly colored additive marketed by E. I. Dupont de Nemours and Company as Dytel, the color of the homogeneous mixture is distorted and the test results are no longer reliable. It is believed that the alkylanilino-substituted anthraquinone dyes in U.S. Pat. No. 3,770,640 are sold under the mark, Dytel. Other leak detectors are disclosed in U.S. Pat. No. 3,370,013 as organic dye compounds such as methyl derivatives of azobenzene-4-azo-2-naphthol, phenyl-azo-2-naphthol and methyl derivatives of azo-benzene-4-azo-2-naphthol, phenyl-azo-2-naphthol, and p-diethylaminoazobenzene.
One homogeneous-type device, identified as "TKO ACID TEST KIT," is simplest to use. It employs a single vial, having a capacity of two fluid ounces, containing a purple mixture of alcoholic potassium hydroxide, an acid-base indicator and a solvent mixture comprising benzene and ethyl alcohol or, preferably toluene and isopropanol. By adding refrigeration oil to the mold line on the neck of the test vial, the correct amount of oil that corresponds to the amount of potassium hydroxide is obtained. The vial need be shaken for only a few seconds after addition of the refrigeration oil sample to produce a homogeneous mixture, with no transfers and no delay for separation into distinct phases. If the test sample has an acid number less than 0.045, the color of the mixture in the shaken vial remains purple. If the oil sample has a borderline acidity, the color becomes orange, indicating that changing the oil is desirable. If the oil is definitely too acidic, the color becomes yellow, indicating that the oil must be changed. Unfortunately, if a red leak detector is present as a component of the refrigeration oil, the results are unreliable.
Another test kit of the homogeneous type is identified "as `ONE TIME ACID TEST KIT` and consists of a two-fluid ounce vial containing an acid-base indicator in a benzene-ethyl alcohol media (reddish-orange in color). A second vial of approximately 0.5 fluid oz., with a capacity for 15.5 g of fresh refrigeration oil, contains an alcoholic potassium hydroxide solution in benzene. According to the test procedure, the contents of the small vial are emptied into the larger vial producing a violet color. The small vial, which also serves as the measuring vial, is then filled with the test oil and finally emptied into the larger vial. If after shaking for fifteen seconds the color of the resulting homogeneous mixture remains purple-red, the oil is considered to be satisfactory". However, if the refrigeration oil contains a highly colored leak detector, the homogeneous mixture does not produce the expected test colors so that the kit is not suitable for such contaminated oils.
A field test kit of the two-phase type, identified as "UNI-KIT", consists of three vials and a glass ampoule containing potassium hydroxide solution. The largest vial has a capacity of approximately one fluid ounce and contains dried crystals of phenolphthalein indicator. When the ampoule is broken and its colorless contents emptied into the large vial with the aid of a small piece of rubber tubing for venting the ampoule and obtaining better drainage into the vial, as described in U.S. Pat. No. 3,653,839, the contents become pink. A second vial, containing isopropyl alcohol and toluene, is emptied into the mixture. Using the third vial for measurement, a sample of the refrigeration oil is then poured into the pink mixture, and the large vial is shaken vigorously. The resulting heterogeneous mixture frequently must stand for one to five minutes so that the partially emulsified layers can be separated sufficiently for an accurate color determination. Any pink color remaining in the bottom layer, even very light pink, signifies satisfactory oil. Therefore, if the oil in the top layer contains a leak detector, such as Dytel, which is even slightly miscible with or emulsified in the bottom layer, a slightly pinkish color is observed which could lead to an erroneous pass for an acidic refrigeration oil which is contaminated with the leak detector.
The fourth test kit, also of the two-phase type, is marketed as "PHASE II" and consists of a two-fluid ounce bottle, which is partially filled with a solvent solution consisting of benzene, methanol, and toluene, and a 0.5-fluid ounce bottle of neutralization solution. When the contents of the smaller bottle are poured into the large bottle, a purple-colored bottom layer is formed. The smaller bottle is then filled completely with oil to be tested and emptied into the larger bottle. After capping and shaking the larger bottle well, the mixture separates into two phases upon standing for two to three minutes. If the bottom layer loses its purple color, the sample has an acid number of 0.05 or more so that the oil should be replaced. This field test kit is probably the most convenient test kit which is now available for testing refrigeration oil taken from a system contaminated with a leak detector, even though it is subject to some interference from the dye. However, there are several practical drawbacks in that the kit requires the use of two bottles instead of only one bottle, considerable time is lost while waiting for phase separation, and benzene as one component of the solvent mixture is now a suspected carcinogen.
Other test kits of interest are described in U.S. Pat. No. 3,528,775 for determining the water content of water-immiscible petroleum products, U.S. Pat. No. 3,449,081 for performing blood tests, and U.S. Pat. No. 1,674,416 for testing alcohol.
In the refrigeration and air conditioning fields, no simple and quickly operated field test kit is known that is not obscured by a leak detector in the oil to be tested. Accordingly, an acid field test kit is needed that provides acidity indications that cannot be obscured by a leak detector in oil contaminated therewith, that requires minimum time for field testing, that requires only a single vial so that transferring liquids is not necessary, and that preferably contains no benzene.